The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having an alloy magnetic layer suitably applicable to a hard disk adapted to carry out recording in an in-plane direction.
In a magnetic recording medium, an alloy magnetic thin film has been noticed as a magnetic material capable of providing good magnetic characteristics such as a high coercive force (Hc) and a high saturation magnetization (Ms) and having a high durability, and the compositions of various such alloy magnetic materials have been studied.
For example, Japanese Patent Laid-open Publication No. 58-7806 discloses a magnetic recording medium composed of Co.sub.x Pt.sub.y alloy, where x is set to 70-90 atomic % and y is set to 10-30 atomic %, the magnetic recording medium having magnetostriction ranging from 35.times.10.sup.-6 through 0 to .+-.10.sup.-6 according to the values of x and y. By setting the above composition, a high Hc of about 1700 Oe and a low magnetostrictive characteristic can be obtained.
Further, Japanese Patent Laid-open Publication No. 58-200513 discloses a magnetic recording medium composed of Co.sub.100-y Pt.sub.y alloy, where y is set to 7-40 atomic %, thereby obtaining a high magnetic flux density (Bs) and a high Hc.
Such a CoPt alloy material has been studied and developed as a material of a magnetic recording medium adapted to carry out recording in an in-plane direction, e.g., a material of a hard disk. However, since Pt is expensive, there is a possibility of an increase in cost for manufacturing the magnetic recording medium.
As another material, Japanese Patent Laid-open Publication No. 61-224124 discloses a magnetic recording medium composed of Co base alloy containing 2-8 atomic % of one or more of Au, Ag, Pd, Rh, Re and Ir. By adding a small amount of Au, Pd, etc. to Co, improvement in corrosion resistance and weather resistance is contemplated, but in some case, a sufficiently desired coercive force of about 1000 Oe or more cannot be obtained depending upon a producing condition such as a burning condition. Further, in the producing step, the Co base alloy is deposited by sputtering or the like in an atmospheric gas containing N.sub.2 gas, wherein a content of N is set to 0.2-5 atomic %. However, it is difficult to control the content of N.
As a magnetic recording material having a perpendicular magnetic anisotropy, Japanese Patent Laid-open Publication No. 1-191318 discloses a magnetic recording medium composed of Co.sub.100-x Pd.sub.x where x is set to 60-90 atomic %, thereby obtaining a good Hc, good rectangular ratio, and improved durability. However, the value of Hc in an in-plane direction is insufficient such as about 200-300 Oe.
Similarly, Japanese Patent Laid-open Publication No. 2-30104 discloses a magnetic recording medium composed of Co.sub.100-x Pd.sub.x where x is set to 50-90 atomic % and a film thickness is set to 1000 .ANG. or less, thereby improving a perpendicular magnetic anisotropy, corrosion resistance and durability. However, also in this case, a high Hc in an in-plane direction is difficult to obtain.
Further, Japanese Patent Laid-open Publication No. 2-3102 discloses a magnetic recording medium composed of an artificial lattice film having an overall thickness of 50-800 .ANG. formed by alternately laminating Co, Pd and Pt, Co and Pd, or Co and Pt, thereby improving a corrosion resistance, durability and perpendicular magnetic anisotropy to obtain a high Hc. However, also in this case, it is difficult to obtain a high Hc in an in-plane direction.